1. Field of the Invention
The present invention relates to an apparatus for inspecting a spark plug connector, and more particularly, to an apparatus for checking a spark plug connector used in internal combustion engines for vehicles such as automobiles.
2. Description of the Prior Art
The spark plug connector electrically connects the terminal of a spark plug (installed in a plug hole) to a high-tension electrical cable extending from a distributor. As shown in FIG. 1, a spark plug connector 6 includes a pipe 3 of circular cross-section, containing a connector terminal 2. The pipe 3 may be formed from resin plastic. One end of the connector terminal 2 is electrically connected to a high-tension electrical cable 1, while the other end is electrically connected to the terminal of a spark plug fitted at the base of a plug hole (not shown). A bushing 4, made of an insulating elastic material such as silicone rubber, is fitted at one end portion of the pipe 3. The bushing 4 covers the external and internal surface of the end portion of the spark plug connector 6. A waterproof cover 5, made of an insulating elastic material such as silicone rubber, is fitted at the other end portion of the pipe 3, closing off the pipe entrance. In this structure, the term "bushing stem" designates the assembly of the pipe 3, the bushing 4 and the waterproof cover 5.
In order to avoid a loose contact between the spark plug and the bushing stem 7 after the bushing stem 7 is assembled, a distance S between the bushing-side rim of the bushing stem 7 and the tip of the connector terminal 2 is measured. The distance S is then assessed as to whether it is within a tolerated range.
As shown in FIGS. 2 and 3, a conventional detection device 8 is used to detect a departure from the tolerances. The detection device 8 includes a bushing holder unit 9 that laterally holds the bushing stem 7 (i.e., in the left and right directions in FIGS. 2 and 3) and a deviation detecting unit 10. The deviation detecting unit 10 is provided to one side of the bushing holder 9 (the right side in FIGS. 2 and 3). The deviation detecting unit 10 is introduced from the side of the bushing 4 of the bushing stem 7 so that the distance S from the bushing 4 to the connector terminal 2 may be measured.
The bushing holder unit 9 includes a fixing plate 11 having a flat rectangular form, and a bushing holder 12 provided at the plug end portion of the fixing plate 11. The bushing holder 12 is formed with a holding recess 12a that holds the bushing 4 in a snug fit and a threshold plate 13. The threshold plate 13 is formed with a (measuring) contact surface 13a for determining the contact position of the end face (rim) of the bushing 4. A waterproof cover holder 14 is fixed on the leftward portion of the bushing holder unit 9, and is formed with a fitting recess 14a that grips the waterproof cover 5. The fixing plate 11 is fixedly provided on a frame portion 15 of the detection device 8.
The deviation detecting unit 10 further includes a mobile base plate 16 fixed to the frame portion 15 of the detection device 8, but freely reciprocable in the axial direction (i.e., the left and right directions of FIGS. 2 and 3). A drive cylinder 17, connected to the frame portion 15, produces an axial thrust that displaces the mobile base plate 16. A measuring probe 19 is mounted on the mobile base plate 16, through a supporting block 18. The measuring probe 19 therefore moves in accordance with the movement of the mobile base plate 16. A distance measuring device 20, including at least an optical sensor or the like, detects the shifted position of the measuring probe 19. The mobile base plate 16 and the drive cylinder 17 are arranged on the frame portion 15 of the detection device 8 such that a tip portion 19a of the measuring probe 19 is in front of and aligns with the corresponding bushing stem 7.
As shown in FIG. 2, the tip portion 19a of the measuring probe 19 is normally set up in a ready-to-trigger position by an elastic or biasing device (not shown), and the tip portion 19a may be thrust towards the bushing holder unit 9 by a predetermined length.
When detecting the deviation in the plug connector 6, the waterproof cover 5 of the bushing stem 7 is retained within the fitting recess 14a of the waterproof cover holder 14, while the bushing 4 is securely pressed into the holding recess 12a of the bushing holder 12.
In this state, the drive cylinder 17 of the deviation detecting unit 10 is actuated toward full extension. The mobile base plate 16 is then shifted towards the bushing holder unit 9. The tip 19a of the measuring probe 19 is passed through an orifice (not shown) formed in the threshold plate 13, and is inserted from the side of the bushing 4 into the bushing stem 7. As shown by the cross-sectional view in FIG. 1, the tip 19a abuts the rim of the connector terminal 2.
If the mobile base plate 16 is further extended from this position, the measuring probe 19 is pushed back toward the distance measuring device 20, against the force of the elastic or biasing device (not shown). The measuring plate 19b provided at the distance measuring device 20 end of the measuring probe 19 approaches the distance measuring device 20.
Subsequently, the distance A between the measuring plate 19b (after being pushed back) and the distance measuring device 20 is measured by the distance measuring device 20, so that the distance S between the rim of the bushing 4 and the tip of the connector terminal 2, and/or deviation from a predetermined distance S, may be indirectly determined. Consequently, it can be determined whether the distance S is within appointed tolerances.
However, in a conventional detection device 8 for plug connector, the bushing holder unit 9 has a bushing holder 12 and a waterproof cover holder 14 specifically modelled on the particular forms of a bushing 4 of the bushing stem 7 and waterproof cover 5 to be inspected. That is, the particular waterproof cover 5 of the bushing stem 7 is retained within a matching fitting recess 14a on the waterproof cover holder 14, while a particular bushing 4 is pressed into a matching holding recess 12a on the bushing holder 12. Thereafter, the deviation of the distance between the rim of the plug connector 6 (specifically, the outside rim of the bushing 4) and the tip of the connector terminal 2 is measured. Moreover, the bushing 4 and the waterproof cover 5 must be pushed to fit onto a pipe 3 of the bushing stem 7. In such a case, depending upon the pushing force, the total length of the bushing stem 7 may vary, causing a distance deviation B between the (measuring) contact surface 13a of the threshold plate 13 and the rim of the bushing 4.
In other words, when measuring the distance S, the rim of the bushing 4 cannot always be placed at a predetermined position, and the distance deviation B often occurs. This distance deviation B leads to measuring error, so that some errors may occur when categorizing conforming and non-conforming products.
Furthermore, in the known devices, a specific type of bushing holder is applied to each different type of plug connector, while each type of plug connector uses a number of types of waterproof cover. Consequently, the conformity of products may be determined by the degree of fit only after the waterproof cover is fitted into the fitting recess. Moreover, each type of bushing holder unit is applicable to one specific type of plug connector and is fixed on the frame portion of the deviation detecting device. In this construction, the bushing holder unit is not amenable for adaptation to various configurations, and therefore cannot be used to measure various plug connectors.